Modern vehicle safety systems are acquiring increasingly as much current data as possible concerning the presence and position of vehicle occupants. Included in this, for example, is that a gas bag is only unfolded when the corresponding seat is also occupied, or else that the gas bag is not released when a child's seat is mounted on the passenger seat. A further important parameter is the distance of the vehicle occupant from the gas bag module, which influences the decision as to whether and, if so, to what intensity an inflation of the gas bag takes place in an accident. Another application which is gaining increasing importance is the monitoring of the driver's fitness to drive. In conceivable future applications, for example the vehicle could be automatically stopped or an emergency doctor could be informed if an unfitness to drive is established.
The sensor arrangement to receive the necessary data is of course to be as robust, as insensitive to breakdown and at the same time able to be manufactured and installed at as favourable a price as possible.
Here, capacitive sensors present themselves which, in quite general terms, detect an alteration to an electric or electromagnetic field, which is brought about by the person who is to be detected. With such sensors, objects can be differentiated from people, if necessary.
Basically, capacitive sensors and their application in vehicle safety systems are described for example in the U.S. Pat. No. 6,254,127 B1. There, a capacitive sensor is provided in the covering cap of a gas bag module arranged in the steering wheel.